1. Field of the Invention
This invention relates to a timepiece of the kind comprising a movement, a dial, indicator means that are rotatably driven about an axis by said movement at the rate of one revolution every twelve hours and which cooperate with said dial to indicate during a first revolution the hours of a first half of a day and during a second revolution consecutive to the first revolution the hours of the second half of the day, and means for differentiating the hours of a first half of a day from the hours of the second half of the day and which include a first transparent region in said dial in a first angular position corresponding to the angular position occupied by said indicator means at a first set hour during said first half of a day and at a second set hour distant from said one set hour by a time interval of twelve hours, an element rotatable about said axis and disposed beneath said dial, a first group of signs disposed on said rotatable element facing said dial the same distance away from said axis as said first transparent region and which include a first sign representing the number of said first set hour and a second sign different from said first sign and representing the number of said second set hour, and means for driving said rotatable element that are connected to said movement and which are arranged to move said rotatable element at a first instant at the start of said first half of a day into a first position in which said first sign faces said first transparent region and at a second instant at the start of said second half of a day into a second position in which said second sign faces said first transparent region, and to maintain said rotatable element in said first position during said first half of a day and in said second position during said second half of the day.
2. Prior Art
Timepieces of the above defined kind are described in many documents such as, for instance, Swiss Patent Specifications 7197 and 18199.
An arrangement that enables one to know whether the hour shown by a timepiece is in the first or second half of a day is for instance useful when the timepiece has a calendar or an alarm which may be set to sound at any time during the twenty-four hours of a day. Such an arrangement enables a user to correctly set such a timepiece, after it has stopped, without fear of having the indications of its calendar changing at noon instead of at midnight or to have the alarm sounding twelve hours too soon or too late.
Timepieces of the above kind have hours and minutes hands that are rotatably driven before a dial by a movement at the rate of one revolution every twelve hours and of one revolution every hour respectively. The dial is not provided with the traditional signs that are used for designating hours but is formed with twelve display apertures that are located where these signs are normally to be found.
A rotary disc, lying beneath the dial, bears numbers 1 to 12 that are evenly distributed along its periphery and numbers 13 to 24 that are evenly disposed between the preceding numbers.
A mechanism that is driven by the timepiece's movement alternately moves the disc to and fro such that each of numbers 1 to 12 will be displayed through one of the apertures in the dial between 1 a.m. and 1 p.m., and that each of numbers 13 to 24 will be displayed between 1 p.m. and 1 a.m. of the next day.
In a modification of this kind of timepiece, described in Swiss Patent Specification 59451, the rotary disc bears numbers 0 to 11 that are visible from midnight till noon, and numbers 12 to 23 that are visible from noon till midnight.
In timepieces of the above kind, having a number-bearing disc that must be alternately moved to and fro complicates the construction and manufacture of the mechanism needed to produce this motion. Further, unavoidable errors in the size of the parts used in the mechanism and in their relative positioning means that it is practically impossible for the disc to move from one position to the other exactly when it should do in theory.